Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpstan/phpstan-phpunit ^1.4.1 -> satisfiable by phpstan/phpstan-phpunit[1.4.1]. - phpstan/phpstan-phpunit 1.4.1 requires phpstan/phpstan ^1.12 -> found phpstan/phpstan[1.12.0, ..., 1.12.11] but it conflicts with your root composer.json require (^2.0.2). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.